Familiar feeling: Yammer’s social-network apps encourage people to collaborate at work the way they communicate with friends online at home. This screenshot is a mockup of Yammer being used by a fictional company.

Some vendors of made-for-business social-network software woo companies from the top down. Jive and IBM’s Lotus Connections, for example, try to sell management on all-encompassing tools such as blogs, wikis, or Facebook-esque profile pages that work well with software already in place at most corporations.

However, the startup Yammer took a bottom-up approach with its collaboration service: it tries to entice rank-and-file employees first and bosses later.

Yammer lets people make microblog posts in a format similar to Twitter or Facebook updates; the users can also message each other, create online groups of colleagues to collaborate, and upload documents. Any person with a company’s e-mail address can join Yammer free. The first person within a company to join can quickly set up a network for the entire company; as coworkers join, Yammer automatically includes them in that company’s network. No involvement from the IT or human resources departments is necessary.

This isn’t to say management is excluded. Eventually, “executives get involved and they start posting,” says David Sacks, Yammer’s CEO and founder. But Sacks lets the software-not a sales associate—convince management that social networks can streamline communications and make people more productive. He also argues that this model spares companies from the risk of investing in expensive software that might not get used much by employees.

Stowe Boyd, an analyst and advisor to companies building social technologies, says Yammer’s method of getting into a company is “revolutionary, subversive.” “Companies turn around and find out that they’ve got 500 people using Yammer, and they want to take control of it,” he says.

For the IT department to gain control, a company has to buy a premium version of Yammer. The premium version also has such features as the ability to link Yammer with employee contact lists and corporate software. Companies generally pay $5 per employee per month for the premium version. (It’s hard to compare this cost with that of rival applications; companies such as Jive and IBM generally customize prices depending on the customer.)

Two million employees at more than 100,000 companies have used Yammer; Sacks says between 15 and 20 percent of those workers are using premium versions.

The join-as-you will structure of Yammer worked well for AAA’s collection of more than 50 regional, independent driving clubs across the United States. Some clubs use it for daily operations and others only for occasional communications, says Janie Graziani, public relations manager of new media and technology at AAA. And the employees who were already reliant on AAA’s intranet system didn’t have to change their ways. “Yammer is just a ‘use this if it’s useful to you and your work’ thing,” Graziani says. “We haven’t told people to use it instead of your e-mail.”

Although Yammer might spread easily in many organizations, the ad hoc way it’s adopted can also create information silos or confusion within a company if too many people are using different tools, says David Coleman, founder of Collaborative Strategies, an industry analysis and advisory services firm. Coleman says he has advised companies that struggled with streamlining their communication tools.

He also says the software will have to show that it increases a company’s profits if it’s going to keep selling itself. “Collaboration itself just for the benefit of interacting really doesn’t have a huge amount of value,” says Coleman. “What it really needs to do is sell the outcomes or the goals that come out of the collaboration.”